Discussions about entry-level, mid-level, and pro-level cameras often revolve around the differences in their sensor size or resolution. However, that's just one aspect of many that separate these types of cameras. Let's take a look at the other benefits that a pro-level camera brings to the table.
APS-C versus full frame is one of the more hotly debated topics among photographers. Discussions on this topic are often centered upon aspects of image quality like dynamic range, low light performance, and high ISO performance. What I don't see discussed often are the benefits of a pro-level camera that don't directly improve your final image quality. Sure, some of these you could attribute to being able to get the photograph in the first place, but I'm talking about actual image capture.
I'm often asked "what camera should I get," which usually turns into quite the discussion. I make sure that I tell people that all modern digital cameras take great photos, but that when you spend more for a pro-level camera, you're often paying for features that don't necessarily contribute to better images, just better operational convenience.
Better Focusing and Viewing
More Focus Points and Groups
When I bought my first full-frame camera, I kept my crop sensor camera and loaned it to my brother-in-law. He shot it for a while and then bought a Canon 80D. When he returned my Canon T3i, I thought I would take it with me to use while my Canon 5D Mark III was doing something else.
It quickly became apparent that I had forgotten just how excellent the 5D Mark III was in comparison. The T3i's nine focus points and 3.7 fps seemed so old-fashioned. Trying to shoot flying birds with a large telephoto lens was simply frustrating.
I gained a whole new appreciation for the Canon 5D Mark III's 61 autofocus points. Along with the number of focus points is the ability to use different autofocus point selections and groups. I'm now shooting a Canon 5D Mark IV, and the one thing I like best about it is being able to assign two buttons for back-button focus. I have one programmed to use whatever point I have manually selected, which I use most of the time. The other I have programmed to use a group of focus points in the middle (large zone AF), which is used occasionally for fast-moving things, such as flying birds. I can switch between the focus modes by simply moving my thumb over one button.
Better Focus Tracking
One of the benefits of having more focus points is the ability to track objects. The more focus points you have, the better the camera can track using those points.
More Viewfinder Coverage
Most crop sensor DSLR cameras have less than 100% viewfinder coverage, usually around 95%. Less than 100% coverage means that the viewfinder isn't showing all of the area that the sensor is going to capture. The result is that you may end up with an image that has things around the edge that you didn't see in the viewfinder but end up in the final image. This means you'll need to crop in post-production.
Shooting and Storage
More Metering Zones and Points
Pro-level cameras often have more metering zone options, such as multiple center-weighted zones and a smaller spot-metering zone. Pro-level cameras also often use more points for metering. For example, the Nikon D850 has a 180,000 pixel RGB metering sensor, whereas the Nikon D750 has a 91,000-pixel RGB metering sensor, and the Nikon D5500 a 2,016-pixel RGB metering sensor.
Pro-level cameras often shoot more frames per second (fps). Entry-level cameras will often have around 4 or 5 fps, whereas a pro-level camera will typically shoot 7 to 10 fps. This may not sound like much of a difference, but when shooting sports and wildlife, it can make quite the difference, especially if you're picky about exactly where that bird's wings are in your photo.
Fps can also make a difference when shooting bracketed photos. The quicker those shots are, the better chance you have of things not moving between shots.
Larger Image Buffer
Along with FPS is the dreaded buffer. Pro-level cameras typically can shoot many more continuous frames before the shooting speed is either reduced or stopped while photos are being written to the memory card.
Dual Memory Card Slots
Perhaps one of the more important features for pro shooters is the addition of dual card slots in the pro-level cameras. Although memory card failures are not very common, many photographers won't shoot important events without the ability to record the images to two cards simultaneously. I rarely shoot to both cards at the same time, but it is nice knowing I have an extra card in the camera for overflow or for transferring images.
More Buttons, Dials, and Joysticks
I like tactile controls. I don't know why, maybe it's just the tech geek in me, but there's just something satisfying about pressing a button or rotating a dial. Pro-level cameras typically have more buttons for specific tasks. I shoot manual mode a lot. Having separate dials for shutter speed and aperture are a joy. You may not realize how much you like them until you go back to a camera that doesn't have a rear dial.
The Customizability of Buttons and Custom Modes
I mentioned earlier about my dual back-button focus setup. This is just one of the features of pro-level cameras, assigning particular functions to different buttons. Being able to program the custom modes is really cool; one turn of the dial and I know exactly what my settings are going to be.
Weatherproofing is something that pro-level cameras have that lower-end cameras typically don't. This could be something to consider if you intend to shoot in adverse conditions that involve rain and/or dust.
I don't think an article would be doing this topic justice if it didn't include at least some mention of the disadvantages of pro-level cameras. They're going to cost more, probably weigh more, be larger, and full frame cameras will have fewer lenses that work with them. I think for most people, these are just accepted things and won't really be an issue, except that cost thing, that's always an issue.
Overall pro-level cameras are, for most people, much more enjoyable to use. You'll most likely see an improvement in image quality, but the benefits go way beyond that. Each photographer will need to weigh the pros and cons of each camera and decide which is best for them.